The rafter legs can be fixed to the Mauerlat or ceiling beams.
The specific decision is made taking into account the individual architectural features of the building. What are the differences between both methods of attaching the rafters?
| Type of fastening rafters | Performance characteristics |
|---|---|
| This method is most often used on buildings made of masonry materials and with concrete attic floors. Mauerlats are installed on the bearing front walls of houses; if necessary, a special reinforcing belt is made to strengthen the support platform of the rafter system. Advantages: the ability to increase the height of the attic by lifting the reinforced belt around the perimeter of the building. Disadvantages - a large bursting load on the facade walls. |
| Recommended for use in cases where load-bearing walls do not differ in high stability indicators. Rafters are attached only to beams in lightweight frame houses made of OSB slabs. Fastening to the floor beams allows not only to remove the expanding loads from the facade walls, but also to distribute them more evenly around the perimeter of the building. Another advantage is that due to several additional stops of the rafter system, you can lighten the structure and make it more stable. This reduces the estimated cost of building a home. Floor beams can be carried out beyond the perimeter of the house by a significant amount, and the emphasis of the rafter legs on these structures increases the area of the attic. |
There is one very important point to consider when designing this type of rafter system. The distance between the floor beams and the rafter legs should be the same, and this parameter depends on several factors.
The decision on the type of fixation of the rafter legs should be made by professionals at the design stage of the house. It should be remembered that the rafter system is considered not only one of the most important architectural elements, but also one of the most complex. Non-professionals should not undertake the installation of the roof, such work can only be performed by experienced builders.
We will consider all possible methods of fixing elements, some of them are used extremely rarely and only during the construction of authentic houses using old technologies. Such work is carried out by top-class carpenters who can work with an ax, chisel, chisel and other traditional carpentry tools.
Special metal mounting plates
Builders use two types of plates. The connection is strong, done quickly and without manual labor. In developed countries, roof trusses of houses are assembled on production lines, and all processes are almost completely automated. Assembly technology makes it possible to increase the productivity of equipment and reduce the cost of production. The elements of the houses on the construction site are quickly assembled, the amount of manual labor is minimized. A turnkey wooden house is built in just two to three weeks, depending on the number of storeys and sizes.
What plates are used to attach rafters to beams?
Toothed
In our country, unfortunately, they are little known, in developed countries they have been used for a long time. Serrated fastening - metal plates with various linear dimensions. There are teeth throughout the area, which are driven into wooden structures. The length and distance between the teeth are selected taking into account the dimensions of the rafter legs and floor beams. Such a connection makes it possible to automate the production process of trusses of the truss system. Serrated plates are installed on both sides of the joint to be connected.
Important. It is possible to use such joints on both sides only on lumber with the same thickness. The maximum deviation is ± 1 mm. It is this condition that does not allow the widespread use of gear joints in our country; most domestic sawn timber does not withstand the required tolerance ranges.
The toothed plates can also be driven in manually, but care must be taken to ensure that they are in the correct position.
Perforated
Well-known fasteners for universal use. They can fix all elements of the rafter system, have various sizes and thicknesses. The plates are applied to the knot, tightening is done with self-tapping screws, bolts or ordinary smooth nails. They can be mounted on one or both sides of the connection. Advantages - there are no strict requirements for the quality of sawn timber, a large number of holes allows you to choose the most successful places for screwing in self-tapping screws. Disadvantages - they require a lot of manual labor. They are harder to work with than toothed ones. In addition, the installation time of the rafter system increases.
Practical advice. The strength of the plate attachment largely depends on the exact adherence to the recommended technology, even minor violations can significantly reduce the stability of the rafter system. In order to eliminate the likelihood of unpleasant situations during the operation of buildings, practitioners recommend tightening the rafter legs and floor beams with crossbars, using vertical posts. These elements compensate for errors in the installation of the rafter system, increase the time and increase the safety of house operation.
Bolt
The roofs of small outbuildings and outbuildings do not have significant loads; during their manufacture, simplified methods of joining rafters and floor beams are used. The most common option is bolted. Holes are made in the floor beams and rafters, the elements are placed side by side, bolts are inserted into the holes, the assembly is firmly pulled together.
Tie-in connection
More complex connections require hands-on construction experience. The insert completely eliminates the possibility of movement of the rafters at the junction with the ceiling beams, the unit is more durable and static. A recess is cut out on the beam, and a ledge on the rafter, the parts must fit tightly into each other.
This method of fixing is done only on the house, which complicates the construction process. In addition, each connection is prepared individually, which further increases the construction time and increases its cost. Another drawback of the tie-in is that each connection reduces the thickness of the rafters and beams, this becomes the reason for a decrease in their bearing characteristics. As a result, designers should, during calculations, provide for increased dimensions of sawn timber, taking into account the reduction in their width as a result of sawing. And this negatively affects the cost of the building.
Cutting connection
An ancient method, nowadays it is used extremely rarely. The work is done by carpenters who know how to handle hand tools and an ax. The cut is made only on thick rafters and beams. An ax, chisel and chisel make a tenon / groove connection at the required angle. The work is physically hard; homemade metal staples can be used as an additional connection. The length of the staples and the diameter of the bar are selected taking into account the specific installation location and the expected maximum load.
Important. A cut-in and cut-out is most often used for a hanging rafter system. Due to the additional fixation, the structure can withstand significant expansion forces.
Practical tips for attaching rafters to floor beams
For example, let's take the most common method of fixing elements, it is suitable for all types of roofs, meets modern requirements for the strength and stability of the assembly. Another advantage is that some work can be done on the ground, and only ready-made structures can be assembled on the building. This method of performing construction work significantly simplifies and speeds up them, the estimated cost of the roof decreases.
The rafters and floor beams are made of planks 150 × 50 mm. The rafter system is the most complex - multi-slope hip. Connecting elements - metal perforated plates. To speed up and simplify the work, it is recommended to prepare a simple, but very functional template made of pieces of boards... How to make a fixture?
- Prepare four pieces of boards 25-30 mm thick. Two pieces about 20 cm long and two 40 cm long.
- Screw two short boards with corners to two long ones, while leaving a gap between them equal to the thickness of the floor board. During the connection, do not join them exactly at the ends, but lift them 2-3 cm from the edge of the long ones. This protrusion serves as an emphasis on the Mauerlat when using the template.
- At a distance of about 30 cm from the bottom, fasten the long boards together with metal perforated plates, to increase strength on the opposite side, pull them together with boards or pieces of plywood. Ensure that the prepared template is rigid and does not wobble during use.
Such a simple device greatly facilitates the execution of the saws of the rafters to connect them to the floor beams.
How to quickly and efficiently make cuts for the connection
During the measurements, we will use a homemade device.
Step 1. Put the fixture on the Mauerlat with short boards, the ceiling beam should be located between them. Small protrusions in the lower part rest against the Mauerlat from the outside. Long boards are strictly vertical and are in line with the plane of the front wall of the house.
Step 2. Screw the attachments to the Mauerlat a little, this will facilitate further work. For screwing it is better to use long and thin self-tapping screws, you do not need to tighten them to the end.
Step 3. Place the rafter cut to length on the upper plane of the floor beam. The corner of the board should rest on the metal plates of the fixture.
The upper part of the rafter should lie in its place, in our case on the diagonal (hip) rafter leg.
After filing, the corner of the rafter leg should lie exactly along the edge of the Mauerlat. It is desirable that the floor beams occupy the same position, but some builders cannot accurately measure their dimensions. Beams come in various lengths and are rarely in position.
Step 4. Measure the horizontal abutment cut line. There are two ways to do this.
- Using the building level. You can use a small tool. Draw a horizontal line from the corner of the rafter leg. Everything is simple, fast and accurate.
- Using a construction square. Measure the distance from the floor joist to the top corner of the rafter leg. Place a square on the plane of the beam and move it until the gap between the beam and the rafter is equal to the same value, in our case 13 cm. Put a mark in the right place. Connect this mark to the corner of the rafter leg. You should get a line parallel to the plane of the floor beam. Take off the board and cut off the excess piece.
The connection will turn out smooth, there will be no protrusions of the rafter legs. Next, you need to take measurements of cutting off the upper part of the rafter leg. For this, the lower section is put in place and held by an assistant. At the junction of the upper part of the ordinary and hip rafters, use a ruler to draw cutting lines. One at a time, press the ruler firmly against the side edges of the hip rafter and mark the vertical lines on both sides.
Apply a ruler and draw a line on the board 
Important. Never mark the upper junction point without filing the lower one. Some inexperienced builders mark the bottom and top of the rafters at the same time, and then cut them off. With this algorithm of work, there will always be gaps; to eliminate them, the rafter will have to be shifted to the side. And this changes the step between them. The fact is that after cutting the lower joint, the abutment angle of the upper node changes.
How to prepare rafters for anchoring on the ground
Real professional builders prepare almost all the elements of the rafter system on the ground according to drawings or templates, number them and, in this form, lift them onto the building. This method of work not only speeds up the construction process at times, but also significantly increases labor safety. It is no longer necessary for carpenters to walk on the temporary flooring many times to take measurements and sawing boards, the connection of the elements is done the first time. But in order to prepare the elements on the ground, you need to have a lot of experience, to carry out the work carefully and responsibly. According to this algorithm, houses are built abroad, the high productivity of workers explains their high, in comparison with domestic, wages. Consider the process of making the simplest roof trusses on the ground for connecting to floor beams.
Step 1. If there are no exact working drawings of the trusses, then a template should be made. It is made from ordinary boards with a thickness of about 25 mm. You need to prepare the template at home, check the correctness in several places. The fact is that masons sometimes make mistakes, due to which the facade walls are not parallel, the spread in the corners can reach several centimeters. This marriage does not affect the fastening of the rafters to the floor beams individually, but in the case of finished trusses, problems may arise.
Step 2. Place the template on a flat area near your home. Bring the first rafter leg and place it on one side of the truss template, align the position.
Step 3. In the same way, place the other leg on the free side of the template. Using a pencil, draw the joining lines of the rafter legs at the top of the truss. Pay attention that the elements do not move during the layout.
Step 4. Use a gasoline or electric saw to cut off any excess planks.
Important. In the upper part of the trusses, the rafter legs will be connected in half a tree, for this you need to make special cuts. You can work with a gasoline saw.
How to properly file the connection?
Practical advice. Such precise filing can only be done with a fully functional gasoline saw with a perfectly sharpened chain. If the sharpening angle is incorrect, then the saw blade is guided to the side, it is impossible to hold the tool evenly with your hands. This saw can only be used when harvesting firewood.
Step 5. Do the same operations with the second rafter. Place the cut legs on the template, check that the cut is correct, correct the position of the boards along the entire length of the template. Everything is OK - Connect the truss legs at the top knot. You can use ordinary nails, it is fast, cheap and reliable.
Step 6. To increase the strength and stability of the truss at the top, fix the legs with a horizontal brace. For these purposes, it is allowed to use thin boards, the element works for breaking, the thickness of 20–25 mm is quite enough to resist the loads. Tensile lumber has high strength values, problems arise when they are compressed. The boards bend, the structure completely loses its stability and original geometric shapes.
Step 7. Use a saw to cut off the lower ends of the rafter legs.
The angle on the template should be such that the connection of the elements is as tight as possible.
It is important to know that with the correct connection of the nodes of the rafter system, the strength of the structure must also be maintained due to the forces of friction between the elements. The boards should be pressed against each other with such force that friction does not allow them to move. What conditions must be observed for this?
- First. The junction plane should be as flat as possible, the area as large as possible.
- Second. The pressing force of the elements must be such that the friction forces reach high values.
In no case should the elements of the rafter system in the attachment points be held only on hardware. It should always be remembered that they are designed to attract the boards, not to hold them. All bolts are rated to break, not shear.
Bend the nails with a hammer (the truss is inverted)
Turned over the truss and template, made markings for trimming the bottom edges
As practice shows, the manufacture of roof trusses and the preparation of joints with floor beams on the ground accelerates the process of building a roof several times. The unit itself can be fixed with metal plates on the sides, nails or bolts in the end, brackets, etc. As already mentioned, to increase the stability of this type of rafter system, it is recommended to install vertical stops between the rafters and beams.
Video - How to saw down rafters at the right angle and the right dimensions
Whether you are using wooden beams in the interior of the house, whether you are making a roof, perhaps building a terrace, you will need information on how to connect wooden beams.
If earlier connections were made using thorns, then this old-fashioned method is gradually becoming a thing of the past, perhaps professionals still use it, but most likely in the near future they will begin to use more modern approaches.
Indeed, in our time, metal connectors allow you to quickly and reliably connect wooden beams. In contrast to screwing, which is also only suitable for certain types of connections, such as diagonal braces. Today, timber beam connectors are available for almost any connection option.
The connectors are manufactured from sheet steel and are pre-drilled. The smaller 3.5mm or 4.5mm holes are great for galvanized V-shaped or comb nails. Some fittings also have larger holes with a diameter of 11 or 13.5 mm. They are used for hex head screws.
Below we will explain which and where the fitting is suitable for connecting wooden beams.
1. T-joints for timber beams
If you want to connect a beam with a standing beam across or, conversely, so that a vertical standing beam is connected to a horizontal one, you can make such a connection in several ways:
Straight connectors are available in lengths from 96 to 180 mm (shown on the left) and are secured with nails or screws.
There are even large straight connectors with lengths of up to 400 mm or even up to 1250 mm - allowing long distance fastening to the beam.
T-beams, also called cross-beams, are suitable for 3-beam T-beams (2 cross beams are stacked side by side on the same post). Typically these types of connections are used in the construction of awnings or terraces.
Such fastenings are used primarily if it is necessary to additionally stabilize the rectangular joints of the beam. They mount at 135 ° and use a variable angle connector to mount at a different angle.
Alternatively, you can use the Universal Connectors (Multi-Function Connectors) with Thigh Slotted ends. These connectors have a predetermined bend point so that they can be adapted to any required angle. Thus, these beam connectors can be used in a wide variety of ways.
Rafter connections are used primarily for roof structures. Particularly strong joist connections are needed here, as they are often exposed to strong winds.
These strong connections are achieved with rafter connectors, which are available in six standard sizes. Such products are made of two types - right and left - so that the beam can be fixed on both sides.
Girder shoes are used when joining a girder to a main girder. These connections are, in particular, the most common when furnishing a room with beams.
This is a particularly strong connection, which is used not only to connect a beam to a beam, but also a beam to concrete or brick, metal.
These connectors are available in various designs: for outside attachment - type A, for inside attachment - type B. The second type allows you to make a more inconspicuous connection, but has a lower torsional rigidity than the first type.
The connection of a beam to a beam that does not correspond to the standard dimensions can be realized using a two-piece connector - Vario (type C).
5. Corner connectors for timber beams
Corner connectors or corner sheets are especially suitable for rectangular timber joints that will not be subject to heavy loads. Therefore, they are often used in the manufacture of furniture and interior decoration.
Corner connectors are available in various sizes and designs, for example as a corner with perforated plate or slotted. Thus, they can be very versatile.
For more stability, special heavy duty connectors must be used.
Cross connectors are used, for example, in the construction of a pergola. To secure this kind of connection between beams, connectors are available in several versions.
Type 1 connectors are very suitable for perpendicular beam connections (see illustration). For oblique cross connections, fork connectors can be used. A slightly more complex option, but also possible, is the use of connectors with two corners (point 5) for heavy loads.
A myriad of joints can be used to connect wooden parts. The names and classifications of joinery and carpentry joints tend to vary significantly depending on the country, region and even school of woodworking. Craftsmanship lies in precision execution to provide a properly functioning joint that is capable of withstanding its intended loads.
Initial information
Connection categories
All connections (in the joinery they are called knitting) of wooden parts according to the field of application can be divided into three categories (foreign version of the classification):
- box;
- frame (frame);
- for rallying / splicing.
Box joints are used, for example, in the manufacture of drawers and cabinetry, frame joints are used in window frames and doors, and joining / splicing is used to obtain parts of increased width / length.
Many joints can be used in different categories, for example butt joints are used in all three categories.
Material preparation
Even planed lumber may need some preparation.
- Trim the material to allow for width and thickness for further planing. Do not cut the length yet.
- Choose the best quality face - the front side. Plan the entire length. Check with a straight edge.
After final alignment, mark the front side with a pencil. - Plan the front - clean - edge. Check with a straight edge and a square against the front. Even out warpedness by planing. Mark the clean edge.
- Using a thickness gauge, mark the required thickness along all edges of the part outline. Reduce the risks to this. Check with a straight edge.
- Repeat the operation for the width.
- Now mark the length and the actual connections. Mark from the front and clean edges.
Lumber marking
Be careful when marking lumber. Make adequate allowances for kerf, planing thickness and joints.
Take all readings from the front side and the clean edge, on which put the appropriate marks. In frame and cabinet designs, these marks should face inward to improve precision. To facilitate sorting and assembly, number the parts on the front side as you make them so, for example, to indicate that side 1 connects to end 1.
When marking the same parts, carefully align them and mark all the workpieces at once. This will ensure that the markup is identical. When marking the frame elements, keep in mind that there may be "right" and "left" details.
Butt joints
These are the simplest joinery and carpentry connections. They can be in all three categories of compounds.
Assembly
The butt joint can be reinforced with nails driven in at an angle. Drive in nails at random.
Cut the ends of the two pieces exactly and join them together. Secure with nails or screws. Before that, you can apply glue to the parts to enhance fixation. Butt joints in frame structures can be reinforced with a steel lining or corrugated key on the outside, or a wooden bar fixed from the inside.
Naggelny / dowel connections
Wooden dowels - today they are increasingly called dowels - can be used to reinforce the connection. These insertion round studs increase shear (shear) strength and use glue to secure the assembly more securely. Connections with dowels (dowels) can be used as frame connections (furniture), drawer connections (cabinets) or for rallying / splice (panels).
Assembly of the dowel joint
1. Carefully cut out all the components to the exact dimensions. Mark the position of the crossbar on the face and clean edge of the rack.
2. Mark center lines for the dowels at the end of the crossbar. The distance from each end should be at least half the thickness of the material. More than two dowels may be required for a wide bar.
Mark the center lines for the dowels on the end of the crossbar and place them on the rack using a square.
3. Lay the Upright and Crossbar face up. Using a square, transfer the center lines to the rack. Number and mark all connections if there are more than one pair of posts and rungs.
4. Transfer this marking to the clean edge of the post and the ends of the crossbar.
5. From the front with a thicknesser, draw a line across the center of the material, crossing the marking lines. This will mark the centers of the holes for the pins.
Using a thickness gauge, draw a center line, crossing the marking lines, which will show the centers of the holes for the dowels.
6. With an electric twist drill or a hand drill with a feather drill, drill holes in all parts. The drill must have a center point and cutters. The hole across the grain should have a depth of about 2.5 times the diameter of the pin, and the hole in the end should have a depth of about 3 times the diameter. For each hole, make a 2 mm allowance, for this distance the dowel should not reach the bottom.
7. Use a countersink to remove excess fibers from the top of the holes. This will also make it easier to install the pin and create space for the adhesive to secure the joint.
Nageli
The dowel should have a longitudinal groove (now standard dowels are made with longitudinal ribs), along which excess glue will be removed when assembling the connection. If the dowel does not have a groove, then shave it flat on one side, which will give the same result. The ends should be chamfered to facilitate assembly and prevent damage from the pins to the hole. And here, if the pins do not have a chamfer, file it or grind the edges of their ends.
Using centrics for marking dowels
Mark and drill the crossbars. Insert special dowel pins into the holes for the dowels. Align the crossbar with the stand markings and squeeze the parts together. The center points will mark the post. Drill holes through them. Alternatively, you can make a template from a wooden block, drill holes in it, fix the template on the part and drill holes for the pins through the holes in it.
Using a jig for a pin connection
The metal jig for dowel joints makes it much easier to mark and drill holes for the dowels. In box connections, the jig can be used on the ends, but it will not work on the face of wide panels.
conductor for naggel joints
1. Mark center lines on the face of the material where you want the stud holes to be. Select a suitable drill guide and insert it into the jig.
2. Align the centering marks on the side of the guide and fix the movable support of the guide bush.
3. Install the jig onto the part. Align the centering notch with the centerline of the dowel hole. Tighten.
4. Place the drilling depth stop on the drill at the desired location.
Rallying
To obtain a wider wooden part, you can use dowels to connect two parts of the same thickness along the edge. Fold the two planks with their wide sides together, line up the ends precisely, and hold the pair in a vise. On a clean edge, draw perpendicular lines to indicate the center lines of each dowel. In the middle of each board's edge, use a thickness gauge to mark across each previously marked center line. The intersection points will be the centers of the pin holes.
The hard connection is neat and durable.
Punch-in / punch-in connections
A cut-in, cut-in or groove connection is called corner or mid-joint, when the end of one part is attached to the layer and another part. It is based on a butt joint with an end cut made in the face. It is used in frame (house frames) or box (cabinets) connections.
Cutting / tapping connection types
The main types of notch joints are the dark / semi-dark T-notch (this term is often replaced by the term “flush / half-flush”), which looks like a butt joint, but is stronger, a quarter-cut corner and a dark / semi-dark corner. The corner cut into the seam and the corner cut into the seam with darkening / semi-darkening are made in the same way, but the fold is made deeper - two-thirds of the material is selected.
Cutting
1. Mark a groove on the face of the material. The distance between the two lines is equal to the thickness of the second part. Continue lines to both edges.
2. Using a thickness gauge, mark the depth of the groove between the marking lines on the edges. The depth is usually made from one quarter to one third of the thickness of the part. Mark the waste material.
3. Use the C-clamp to secure the part securely. Saw off the shoulders on the retreating side of the scribe lines to the desired depth. If the groove is wide, make additional cuts in the back to make it easier to cut the material with the chisel.
Saw in the runway to the scoring line on the retract side, making intermediate cuts with a wide notch.
4. Using a chisel on both sides, remove excess material and check the bottom for flatness. You can use a soil tube to level the bottom.
Use a chisel to remove waste by working on both sides and line the bottom of the groove.
5. Check the fit, if the part is too tight you may need to trim it. Check for squareness.
6. The cut connection can be strengthened in one of the following ways or a combination of them:
- gluing and clamping until the glue sets;
- screwing with screws through the face of the outer part;
- nailing at an angle through the face of the outer part;
- nailing obliquely across the corner.
The cut connection is strong enough
Groove and side flange connections
It is a combination of quarter cut and rebate cut. It is used in the manufacture of furniture and the device of the slopes of window openings.
Making a connection
1. Make the ends perpendicular to the longitudinal axes of both parts. On one part, mark the shoulder by measuring the thickness of the material from the end. Continue marking on both edges and the front side.
2. Mark the second shoulder from the butt end, it should be one third of the material thickness. Continue to both edges.
3. Using a thickness gauge, mark the groove depth (one third of the material thickness) at the edges between the shoulder lines.
4. Using a backed hacksaw, cut through the shoulders to the notches of the thicknesser. Remove waste with a chisel and check alignment.
5. Using a thickness gauge with the same setting, mark a line on the back and on the edges of the second part.
Advice:
- Groove and side flange connections can be made easily with a router and an appropriate guide - either for the groove only, or for both the groove and rebate. For recommendations on correct work with the router see p. 35.
- If the comb fits too tightly into the groove, trim the face (smooth) side of the comb or sand with a sandpaper.
6. From the front side, use a thickness gauge to mark the edges towards the end and at the end itself. Saw along the lines of the planer with a backed hacksaw. Do not cut too deep as this will weaken the joint.
7. Working with the chisel from the end, remove the waste. Check fit and correct if necessary.
Half-wood connections
Half-wood joints refer to frame joints that are used to join parts with faces or along an edge. The connection is made by sampling the same amount of material from each part so that they are joined flush with each other.
Half-tree connection types
Six main types of half-wood joints can be distinguished: transverse, angular, dark, angular, dovetail, and splice.
Making a corner joint in half a tree
1. Align the ends of both parts. On the top side of one of the parts, draw a line perpendicular to the edges, stepping back from the end by the width of the second part. Repeat on the underside of the second piece.
2. Set the thickness gauge to half the thickness of the pieces and draw a line at the ends and edges of both pieces. Mark the waste on the top side of one and the bottom side of the other part.
3. Clamp the part in a vice at a 45 ° angle (face up). Saw carefully along the grain, close to the thicknessing line on the retract side, until the saw is diagonal. Turn the piece over and continue cutting gently, gradually raising the saw handle until the saw is in line with the shoulder line on both edges.
4. Remove the part from the vise and lay it down. Press it firmly against the tsulag and clamp it with a clamp.
5. Saw through the shoulder to the previously cut and remove the waste. Align all unevenness of the sample with a chisel. Check the cutout for neatness.
6. Repeat the process for the second part.
7. Check fit of the parts and level with a chisel if necessary. The connection must be rectangular, flush, without gaps and backlash.
8. The connection can be strengthened with nails, screws, glue.
Mustache corner joints
Corner bevels are made using the bevel of the ends and hide the end fiber, and also aesthetically correspond more to the angular rotation of the decorative strip.
Types of corner joints with a mustache
To perform bevelling of the ends in a gusset, the angle at which the parts meet is halved. In a traditional joint, this angle is 90 °, so each end is cut at 45 °, but the angle can be both obtuse and sharp. In uneven corner joints, parts with different widths are connected to the mustache.
Making a corner connection with a mustache
1. Mark the length of the parts, keeping in mind that it should be measured along the long side, as the bevel will reduce the length inside the corner.
2. Having decided on the length, mark a line at 45 ° - on the edge or on the face, depending on where the bevel will be cut.
3. Using the combination square, transfer the marking to all sides of the part.
4. For hand cutting, use a miter box and backed hacksaw or hand-held miter saw. Press the part firmly against the back of the miter box - if it moves, the bevel will turn out to be uneven, and the joint will not fit well. If you are simply sawing by hand, follow the process so as not to deviate from the marking lines on all sides of the part. A miter saw, if you have one, will make a very neat bevel.
5. Place two pieces together and check fit. You can correct it by trimming the surface of the bevel with a plane. Fix the part firmly and work with a sharp plane with a small overhang of the knife.
6. The connection should be knocked down with nails through both parts. To do this, first put the parts on the face and hammer nails into the outside of the bevel so that their tips barely appear from the bevels.
Place nails in both parts so that the tips stick out slightly from the bevel surface.
7. Apply glue and firmly squeeze the joint so that one part protrudes slightly - overlapping the other. Drive nails into the protruding part first. Under the blows of the hammer, when hammering in the nails, the part will move slightly. The surfaces should be leveled. Nail the other side of the joint and sink in the nail heads. Check the squareness.
First, drive nails into the protruding part and the hammer will push the joint into position.
8. If, due to the roughness of the design, there is a small gap, iron the joint on both sides with a round screwdriver shank. This will move the fibers, which will close the gap. If the gap is too large, then you will either have to redo the connection, or seal the gap with putty.
9. To strengthen the corner joint, a wooden block can be glued into the corner on the mustache, if it will not be visible. If appearance is important, then the connection can be made on a plug-in dowel or secured with veneer dowels. Inside flat connections, pins or lamellas (standard flat dowels) can be used.
Mustache splices and cut join
A mustache splice connects the ends of parts located on the same straight line, and a cut-off connection is used when it is necessary to connect two profile parts at an angle to each other.
Splicing on a mustache
When splicing on a mustache, the parts are connected with the same bevels at the ends in such a way that the same thickness of the parts remains unchanged.
Cut-off connection
The connection with a cut (with undercut, with a fit) is used when it is necessary to connect two parts with a profile in a corner, for example, two skirting boards or cornices. If the part moves during the fastening process, then the gap will be less noticeable than with a gusset.
1. Fasten the first skirting board in place. Slide the second skirting board along the wall to it.
Secure the first skirting board in place and press the second skirting board against it, aligning it along the wall.
2. Draw a small piece of wood with a pencil pressed against the profile surface of the fixed plinth. The pencil will leave a marking line on the skirting board to be marked.
With a bar with a pencil pressed against it, with a tip attached to the second plinth, draw along the relief of the first plinth, and the pencil will mark the cut line.
3. Cut along the scribed line. Check fit and adjust if necessary.
Complex profiles
Place the first skirting board in place and, placing the second skirting board in the miter box, make a bevel on it. The line formed by the profile side and the bevel will show the desired shape. Cut along this line with a jigsaw.
Eyelet connections
Eyelet connections are used when you want to connect intersecting parts that are "On Edge", either in a corner or in the middle (for example, a corner of a window sash or where a table leg meets a bar).
Types of eyelet connections
The most common types of lug connections are angled and tee (T-shaped). For strength, the connection must be glued, but you can strengthen it with a dowel.
Making a lug connection
1. Make the same lines as for, but divide the thickness of the material by three to determine one third. Mark waste on both parts. On one part, you will need to choose the middle. This groove is called an eyelet. On the second part, both side parts of the material are removed, and the remaining middle part is called a thorn.
2. Cut along the grain to the shoulder line along the outgoing side scribble lines. Use a hacksaw with a backing to cut out the shoulders, and you get a thorn.
3. Working on both sides, select the material from the eyelet with a chisel / slot chisel or jigsaw.
4. Check fit and correct with a chisel if necessary. Apply glue to the joint surface. Check the squareness. Use a C-clamp to clamp the joint while the adhesive hardens.
Thorn-to-socket connection
Stud-to-socket joints, or simply finger joints, are used when two parts are joined at an angle or at an intersection. It is probably the most durable frame joint in joinery and is used in the manufacture of doors, sashes and furniture.
Types of spike-to-socket connections
The two main types of tenon joints are the conventional tenon-to-socket connection and the stepped tenon-to-socket connection (semi-dark). The spike and socket are approximately two-thirds the width of the material. The expansion of the socket is done on one side of the groove (semi-dark), and a step of the thorn is inserted into it from its corresponding side. The semi-dark helps to prevent the spike from turning out of the nest.
Plain spike-to-socket connection
1. Determine the joint position on both parts and mark on all sides of the material. The markup shows the width of the intersecting part. The spike will be at the end of the bar and the socket will go through the post. The spike should have a slight allowance along the length for further stripping of the joint.
2. Select a chisel as close as possible to a third of the material thickness. Adjust the thickness gauge to the size of the chisel and mark the socket in the middle of the rack between the previously marked marking lines. Work from the front. If desired, you can set the thicknessing solution to a third of the thickness of the material and work with it from both sides.
H. In the same way, mark the cleat on the end and both sides until the shoulders are marked on the bar.
4. Clamp the trim support support in a vise high enough to attach the ribbed post to it. Attach the stand to the support by placing the clamp next to the nest markings.
5. Use a chisel to cut a nest, making an inward allowance of about 3 mm from each end, so as not to damage the edges when cutting waste. Keep the chisel straight while keeping it parallel
its edges are the plane of the rack. Make the first cut strictly vertically, with the sharpening bevel towards the middle of the nest. Repeat from the other end.
6. Make several intermediate cuts, holding the chisel at a slight angle and beveling the sharpener down. Select a retreat by acting as a lever with the chisel. Deeper 5 mm, make more cuts and select a retreat. Continue to about half the thickness. Turn the piece over and work the same way on the other side.
7. After removing the bulk of the waste, strip the socket and cut the allowance left earlier to the scoring lines on each side.
8. Cut a thorn along the grain by guiding the backed hacksaw along the line on the retreat side and cut out the shoulders.
9. Check fit and adjust if necessary. The shoulders of the cleat must fit neatly to the post, the connection must be perpendicular and free of play.
10. For securing, wedges can be inserted on both sides of the cleat. A gap for this is made in the socket. Using the chisel from the outside of the socket, extend approximately two-thirds of the depth with a 1: 8 slope. Wedges are made with the same bias.
11. Apply glue and squeeze firmly. Check the squareness. Apply glue to the wedges and press them into place. Saw off the cleat allowance and remove excess glue.
Other spike connections
Tongue joints for window sashes and doors are somewhat different from half-dark finger joints, although the technique is the same. Inside there is a rebate and / or an overlay for glass or infills (panels). When making a tenon-to-socket connection on a rebated part, make the plane of the tenon in line with the rebate edge. One of the shoulders of the crossbar is made longer (by the depth of the fold), and the second is shorter, so as not to block the fold.
Studded joints for parts with overlays have a shoulder that is cut to fit the profile of the overlay. Alternatively, you can remove the trim from the edge of the socket and make a bevel or cut to match the mating piece.
Other types of spike-to-socket connections:
- Side spike - when making doors.
- Concealed half-dark beveled thorn (with a beveled step) - to hide the thorn.
- With a thorn in the dark (thorn steps on both sides) - for relatively wide parts, such as the lower rail (bar) of the door.
All these connections can be through, or they can be blind, when the end of the tenon is not visible from the back of the rack. They can be reinforced with wedges or dowels.
Rallying
Wide, high quality timber is becoming more difficult to find and very expensive. In addition, such wide boards are subject to very large shrinkage deformations, which makes it difficult to work with them. To join narrow boards along the edge into wide panels for countertops or workbench covers, rallying is used.
Preparation
Before starting the direct rallying, you must do the following:
- If possible, select radial cut boards. They are less susceptible to shrinkage than tangential sawn timber. If tangential sawing boards are used, place their core side alternately on one side and the other.
- Try not to bundle materials with different sawing methods into one panel.
- Under no circumstances should boards from different types of wood be pulled together if they are not properly dried. They will shrink and crack differently.
- If possible, arrange the boards with the fibers in one direction.
- Be sure to cut the material to size before seaming.
- Use only good quality glue.
- If the wood will be polished, match texture or color.
Rallying for a smooth puffer
1. Place all boards face up. For easy reassembly, mark the edges with a continuous pencil line drawn at the seams at an angle.
2. Sew straight edges and check fit to the corresponding adjacent boards. Align the ends or pencil lines each time.
3. Ensure that there are no gaps and that the entire surface is flat. If you compress the gap with a clamp or putty it, the joint will subsequently crack.
4. When slicing short pieces, clamp the two sides together in a vise and plane both edges at the same time. It is not necessary to maintain the rectangularity of the edges, since when joining they will mutually compensate for their possible inclination.
5. Prepare as for butt joint and apply adhesive. Squeeze and lapping, connect the two surfaces, squeezing out excess glue and helping the surfaces to "stick" to each other, as it were.
Other ways of rallying
Other rallying joints with different reinforcement are prepared in the same way. These include:
- with dowels (dowels);
- in the groove and comb;
- in a quarter.
Bonding and clamping
Bonding and fixing glued parts is an important part of woodworking, without which many products will lose strength.
Adhesives
The adhesive reinforces the connection by holding the parts together so that they cannot be easily separated. Always wear protective gloves when handling adhesives and follow the safety instructions on the packaging. Remove excess glue from the product before it sets, as it can blunt the planer knife and clog the abrasive skin.
PVA (polyvinyl acetate)
PVA glue is a universal glue for wood. While still wet, it can be wiped off with a cloth dampened with water. It perfectly adheres to loose surfaces, does not require long-term fixation for setting and sets in about an hour. PVA gives a fairly strong bond and adheres to almost any porous surface. Gives a permanent bond, but is not heat and moisture resistant. Apply with a brush, and on large surfaces dilute with water and apply with a paint roller. Since PVA glue is water-based, it shrinks when set.
Contact adhesive
Contact adhesive sticks together immediately after application and joining of parts. Apply it to both surfaces and when the glue is dry to the touch, bond them together. It is used for laminated plastic (laminate) or veneer to chipboard. No fixation required. Cleaned off with solvent. Contact adhesive is flammable. Work with it in a well-ventilated area to reduce the concentration of vapors. Not recommended for outdoor use, as it is not moisture and heat resistant.
Epoxy adhesive
Epoxy is the most durable and most expensive woodworking adhesives available. It is a two component resin based adhesive that does not shrink when set and softens when heated and does not creep under load. It is waterproof and adheres to almost all materials, both porous and smooth, with the exception of thermoplastics such as polyvinyl chloride (PVC) or plexiglass (organic glass). Suitable for outdoor use. In an uncured state, it can be removed with a solvent.
Hot glue
Hot melt adhesive will bond almost everything, including many plastics. It is usually sold in the form of glue sticks that are inserted into a special electric glue gun. Apply glue, bond surfaces and squeeze for 30 seconds. No fixation required. It can be cleaned off with solvents.
Clamps for fixing
Clamps come in a variety of designs and sizes, most of which are called clamps, but usually only a couple are required. Be sure to place a wood waste gasket between the clamp and the work to avoid pressure dents.
Bonding and fixing technique
Before gluing, be sure to assemble the product "dry" - without glue. Lock as necessary to check connections and dimensions. If everything is normal, disassemble the product, placing the parts in a convenient order. Mark the areas to be glued and prepare the jaws / jaws with the required distance.
Assembling the frame
Spread the adhesive evenly on all bonding surfaces with a brush and quickly assemble the product. Remove excess adhesive and secure the assembly with clamps. Compress the joints with even pressure. The clamps should be perpendicular and parallel to the product surfaces.
Place the clamps as close to the joint as possible. Check the parallelism of the crossbars and align if necessary. Measure the diagonals - if they are the same, then the rectangularity of the product is maintained. If not, then a light but sharp blow to one end of the rack can flatten the shape. Adjust the clamps if necessary.
If the frame does not lie flat on a flat surface, tap the protruding areas with a mallet through a wooden block as a spacer. If this does not work, you may need to loosen the clamps or use the clamps to secure the block of wood across the frame.
Particular attention must be paid to the strength of the supporting roofing systems, since the protection of the building from bad weather depends on it. Mistakes made when attaching the rafters to the beams are fraught with big troubles, up to the repair of the roof or even its dismantling and the creation of a new frame. Roof beams are an indispensable part of the entire roof structure. They are made of wood and metal; there is also a reinforced concrete rafter beam on sale.
When developing a roof project and when creating it, many factors are taken into account that create loads on the rafter structures, among them:
- the weight of the coating and other elements of the roofing "pie";
- wind strength;
- the greatest possible thickness of snow on the roof;
- the presence of equipment and other loads on the frame.
The main elements of the roofing structure, which bear the most loads, include:
- rafter system or truss;
- split beams.
Of course, the quality of the material from which the above materials are made is of great importance, but no less important is the strength and reliability of the connection of the roof elements to each other.
I-beams
I-beams are a structural material that is used for the construction of buildings using frame technology, as well as for the construction of floors. They do not have the disadvantages inherent in wood, and due to the presence of an I-section, high strength characteristics are achieved. Docking of I-beams is done using a carpentry tool.
Methods for attaching rafters to walls
Today, the main options for installing rafters and attaching them to the walls of houses are as follows:
Fasteners for rafters
For the assembly of the truss structure, wooden elements and metal products are used. Wooden fasteners include: bars; triangles; dowels, etc.
Metal fasteners are nails, bolts, steel corners, screws, studs, clamps, staples, special rafter devices called sleds or sliders, and more.
WB Beam Fasteners are used in the installation of load-bearing beams for wooden structures in the construction of wooden houses. Its advantage is that there is no need to cut into the beam, and the fastening is done with nails, screws or anchor bolts.
Methods for attaching the rafters to the Mauerlat
The most common way of attaching the rafters at the bottom is considered to be their connection to the Mauerlat (read: ""). Despite its popularity, not every builder will succeed in performing such work with high quality, and this cannot but affect the strength and reliability of the roof.
Before attaching the rafters to the Mauerlat beams, a special cutout is made at the bottom of the rafter leg. It is impossible to install the rafters without this, since at the slightest load the flat edge of the timber will slide off the surface of the beam. As for the recess in the Mauerlat, whether to do it or not depends on the material of its manufacture.
In the case of using hardwood, experts recommend making an incision in the beam - it, together with the slot made in the rafter leg, will create a persistent lock. When the Mauerlat is made of softwood, it is undesirable to make cuts, as they will lead to a weakening of the structure. The condition of the roof in different weather conditions depends on the way in which the beams are fastened to the Mauerlat (read more: "").
The connection of the beam to the rafter leg
The roof of the house, under the influence of loads on it, tends to part to the sides and down. To prevent this, various design solutions are used to prevent the displacement of the elements of the roof frame.
This is how the cutting of the notches in the rafter leg was invented, which can be done using such connections as:
- tooth with one stop;
- a tooth with a spike and an emphasis;
Fastening the rafters to the Mauerlat, see the video:
A single-tooth cut is used when the roof has a large slope angle. This means that the rafters are attached to the floor beams at an angle of more than 35 degrees. A tooth with a thorn is cut out in the leg, and a nest is created in the beam for the entrance of the thorn. In this case, the depth of the groove cannot be more than 1/3 or 1/4 of the beam thickness, otherwise the element weakening occurs. The cut is made, stepping back from the edge of the beam 25 - 40 centimeters, then it will be possible to avoid the likelihood of chips. In order to prevent the joint from shifting to the side, a single tooth must be created together with a spike.
A double-tooth cut is performed for shallow roofs, when the angle between the connection elements does not exceed 35 degrees, it is performed in one of the following ways:
- two thorns;
- an emphasis without a thorn;
- emphasis supplemented with a spike;
- lock-type connection with two spikes and other options.
The insertion depth is usually the same for both teeth. But in some cases, the first tooth supplemented with a spike is cut in 1/3 of the beam thickness, and the second - 1/2.
When creating roofs, there is such a method of constructing rafters, when the rafter legs and wooden ceiling beams are connected, but it is rarely used. In this case, a stop tooth is cut out in the leg so that one of its planes rests on the flat edge of the beam, and the other plane rests against the gash made 1/3 of the beam thickness deep. For reliability, in addition to the cut, an additional connection is made using clamps, bolts, wire loops or metal strips.
Roof ridge connection
Currently, in the construction industry, when creating a rafter system, 3 methods of connecting rafters on a ridge are used:
- butt joint;
- installation on a ridge girder;
- fastening with an overlap on a ridge girder.
To understand which option is preferable, you need to figure out how they are performed.
Butt joint ... The upper part of the rafter leg is cut at an angle that is equal to the angle of inclination of the roof and rests it on the other rafter leg, on which the trim is also performed only in the opposite direction. This work is performed according to a pre-made template. In some cases, to provide more stress in the stop, trimming is performed during installation, while the cut is made through both bars, as a result of which the two planes fit snugly against each other. Then the rafters are connected to each other using long nails.
When this method is used, a metal or wooden lining is used for additional fastening - it is installed with bolts or nails are hammered in at the junction.
Installation on a ridge girder ... This method is very similar to the previous method. The difference lies in the installation of the ridge beam. This one is reliable, but it is not always possible to use it, since additional installation of support beams is required here and then the attic is not very convenient to use.
This option allows you to carry out the work of installing each pair of rafter legs directly on site without preliminary work and the use of templates. The upper edge of the leg in this case rests against the ridge beam, and the lower edge against the Mauerlat.
Fastening with an overlap on a ridge girder ... The work is carried out similarly to the previous option, only the upper joint of the rafters is overlapped. They touch at the top not with their ends, but with their sides. The fasteners are bolts or studs.
Repair of roof structures
A private house can be operated for more than a dozen years and often a situation arises when it is necessary to repair the elements of the truss structure. The condition of the roof frame and roof covering must be constantly monitored, since their destruction leads to great trouble. If defects are found, emergency measures must be taken.
Problem: the end of the rafter leg began to rot based on the Mauerlat. In such a situation, a log is placed on the ceiling of the attic; it must rest on several beams (the installation of the floor beams must be reliable). Under the repaired rafter leg, they put struts - it is necessary that they rest against the log. The distance between the extreme strut and the place of decay should exceed 20 centimeters. After the damaged section has been removed by sawing out, a previously prepared insert is mounted in its place.
Problem: Wood rot was found in the middle of the rafter leg ... In order to strengthen the rafter structure, on both sides of the damaged element, wooden plates from boards 50-60 millimeters thick are nailed. Fastening nails are driven along their edges into the intact part of the rafter.
Problem: damaged mauerlat ... When this is an insignificant area, experts advise installing struts with a rafter leg attached to them with brackets. The braces are mounted with support on the undamaged part of the Mauerlat. In the event that the area of damage to the Mauerlat is significant, then a lining of boards is nailed to the rafter leg, they, in turn, are attached to a new Mauerlat, which is installed slightly lower than the damaged one. An additional Mauerlat is mounted into the wall using pins, while performing in accordance with the project.
Problem: a crack has appeared in the rafter leg , as a result of which there was a deflection of the roof. To carry out the repair, you need to prepare 2 boards, one of them will become a squeeze rack, and the second - a support for it. The support board is fixed perpendicular to the attic floor beams. The squeeze rack is installed on a previously fixed support and brought it under the deflection of the leg. Between the end of the squeeze rack and the support board, 2 wedges are driven in one towards the other. They continue to hammer until the deflection is eliminated. At the place where the crack is located, two boards are applied, the length of which is at least one meter longer than the size of the damaged area. They are bolted in place. Then the wedges are knocked out, the support board and the temporary stand are removed.
Problem: reinforcement of the rafter system is required because the new roofing material is heavier than the old one. To do this, the main section of the rafters is increased, building it up with boards. What value needs to be increased (but not more than 5 centimeters) is determined by calculations (see also: ""). The gasket and the rafter are connected using nails.
Beam element joints
Features of factory, enlargement and assembly joints. The need for the arrangement of joints of the elements that make up the beam may arise, firstly, due to the insufficient length of sheets and corners rolled at the factories, in comparison with the length of the beam and, secondly, due to the fact that the total weight of the beam or overall dimensions it is not allowed to transport or lift entire beams with the equipment available at the construction site.
In the first case, the joints of individual elements are arranged during the manufacture of the beam at the factory and therefore are called factory. In the second case, the joints of the parts of the beams are performed at the enlarged assembly sites, and in case of insufficient loading capacity of the assembly equipment, at the site of the permanent location of the structure. The first of them are called enlarged joints, and the second ones are called assembly joints.
The position of the joints of individual elements, made at the factory, depends mainly on the length of these elements. The length of the wide sheets used on the wall and the narrow ones going to the belts, as well as the corners, are different, therefore, factory joints are arranged in different places with beams, or, as they say, in bulk. Independent joining of individual elements in the manufacture of a beam does not cause any particular difficulties. The factory joints of the sheets in the belts and walls are welded before the belt seams are applied, which ensures freedom of deformation during the cooling of the joints, as well as the simplicity of the arrangement of the joints themselves and their subsequent processing, if required. In order to reduce the number of templates for the manufacture of individual elements, it is useful to arrange their joints symmetrically relative to the middle of the beam span. This creates more repeatability of the elements.
All longitudinal elements of the beam are connected in the enlargement and assembly joints. The relative position of these elements at the time of the joint is strictly fixed. Due to their large size and weight, rotations of the parts to be joined are difficult during pre-assembly, and completely impossible during assembly. Therefore, when designing such joints, the conditions of work and the availability of individual elements for welding or setting bolts (rivets) should be carefully taken into account.
In addition, for the convenience of transporting individual sections of beams and reducing the risk of damage to their elements, it is desirable that the latter do not form protruding parts (overhangs).
The fastening of each element of the beam at the joint must be calculated for the force factors acting in this element (N, Q or M).
Joints in welded beams. When designing joints, the order in which the beam elements are welded must be taken into account. This order should be such as to ensure the greatest freedom of deformation and movement of individual elements to be connected and thereby reduce the magnitude of shrinkage stresses. For this purpose, as noted above, the factory welding of the belts and walls is carried out separately, and then the belts are connected to the wall; in the enlargement and assembly joints of the beams, the belt seams are not brought to the joint by about 50 cm (Fig. IV-18, b, c). It also shows the recommended sequence of welded joints at the beam joint to reduce the harmful effect of shrinkage stresses.
In beams of variable cross-section, the joints of the flange sheets are usually used to change their width or thickness. In a multi-sheet package, the joints of individual tapes should be staggered.
The most rational type and the only acceptable in beams operating under a dynamic load is a joint of sheets without overlays (Fig. IV-18, a). Butt joints reinforced with overlays require more metal (base and weld metal), more time and labor, and the endurance limit of seams with overlays is lower than without overlays. Joints that are only bridged with overlays have a particularly low endurance limit.
In the compressed chord of the beam, all butt seams are arranged at right angles to the longitudinal axis. If the quality of stretched butt welds can be checked by gamma ray transmission or other enhanced control methods, then such seams can be arranged straight anywhere in the beam. Butt seams, if they are located in places with tensile stresses σ> 0.85R, should be X-rayed in the stretched belt and in the adjacent part of the wall at a length of about 1/10 of the wall height. If it is impossible to use increased control means, stretched joints are arranged straight in places with stresses σ≤0.85R or oblique with an angle σ = 65 ° between the direction of the seam and the longitudinal axis of the element (leg ratio 2.1: 1).
If the calculated tensile stress of the straight butt joint of the wall is more than Rp sv = 0.85R, but the stretched belt in this place does not have a joint or its welded joint is equal in strength to the belt, then the wall seam will work under constrained deformation conditions. Therefore, in a limited area adjacent to such a belt, one can not be afraid of the harmful consequences of design overvoltages and leave the wall seam straight.
In the manufacture of beams designed for static loads, in workshops that do not have equipment for precise cutting of sheets and preparation of edges for seams into a joint, as well as with large gaps between the joining parts of the beams on installation, it is permissible to overlap the joints of the wall sheets and chords only with overlays. The joint of the wall sheets is covered with two rectangular overlays (Fig. IV-18, d), welding them with fillet seams. The thickness of the overlays at the wall is usually the same as the thickness of the wall. In this case, two shallow frontal seams (1: 1.5), laid along the long sides of the linings, have a greater load-bearing capacity than the wall:
Therefore, there is no need for flank seams. It is difficult to arrange flank seams if belts are welded to the wall. The width of the linings is assigned about 10 of their thicknesses (to reduce the effect of shrinkage stresses and for a smoother deflection of power flows).
The strength of fillet welds should be checked because the length of the overlays is less than the full height of the wall.
The belts are covered with overlays. One-sided linings cause a sharp deflection of power flows and deterioration of the belts. The thickness of the overlays is determined by the required height of the fillet welds; in this case, the cross-sectional area of the lining must be not less than the cross-sectional area of the sheet to be covered. In the places where one-sided pads are attached to the belt, the height of the belt seams should be slightly increased in order to reduce the adverse effect of eccentricity at the joint.
The calculation of fillet welds attaching the lining to the flange plates is carried out either according to the force acting in the sheet at the junction N = Fσ, or according to the bearing capacity of the sheet [N] = FR:
where ΣFsh is the calculated area of fillet welds located on one side of the joint.
Considering the presence of eccentricity at the joint with a one-sided lining, it is useful to increase the design force by about 20%.
The seams that attach the pads to the wall are calculated by the bending moment Mst acting in the wall:
where ΣWsh is the sum of the moments of resistance of fillet welds located on one side of the joint.
The magnitude of the bending moment Mst falling on the beam web is determined from the proportionality between the bending moments falling on the individual parts of the composite beam and the stiffnesses of these parts:
where Ist, Ip and Ib are the moments of inertia of the wall, belt and the entire beam relative to the neutral axis of the beam;
Mb - bending moment acting on the beam at the joint.
The seams connecting the strips to the wall must also be tested for the effect of a lateral force acting at the joint. Due to the low rigidity of the chords of the beams in comparison with the wall, it is believed (as a margin of safety) that the entire transverse force is taken up by the seams at the wall linings. Average shear stress in seams:
where ΣFsh is the sum of the areas of fillet welds located on one side of the joint.
Although the maximum stresses from the shear force do not coincide with the maximum stresses from the bending moment, they make a conditional check of the strength of the seams for the effect of both force factors:
Beam connections
You can connect the beams to each other in very different ways. The choice of the connection method depends on the relative position of the beams, on the force factors and on the connection means used.
Crossing beams can be positioned one above the other or at the same level. In addition, adjoining beams are sometimes positioned obliquely in relation to the main beams in a horizontal or vertical plane.
Joints of beams that transmit only support pressures are called free (hinged). Connections that transmit both bearing pressures and bearing moments are called rigid (pinched) connections.
When designing the connections of the main and secondary beams, it should be borne in mind that in most cases the latter are used as ties that ensure the overall stability of the main beams.
The easiest way is to fasten the beams with a storey arrangement.
Under the nuts of the bolts adjacent to the flanges of I-beams and channels, oblique washers should be placed from the inside in order to eliminate the bending of the bolts in the cut part of them.
The places in which heavily loaded auxiliary ones rest on the composite beams should be reinforced with stiffeners tightly fitted to the upper chord to eliminate local overstressing of the belt seams and the wall. In such cases, the rolling beams should be checked for wall compression under the fillet connecting it to the flange. In case of overvoltage, ribs must be installed.
Beam connections at the same level and lowered are divided into fixings that do not require precise cutting of auxiliary beams and require accurate cutting them. The latter are very laborious and therefore undesirable.
Auxiliary beams, located at the same level or lowered, are conveniently attached to the transverse ribs of the main beam using bolts (Fig. IV-19, a). In this case, one or both flanges of the auxiliary beams and part of the wall have to be cut off. The vertical and horizontal parts of the cut are mated by rounding with a radius of about 20 mm. Such fastening does not require precise cutting of auxiliary beams and is convenient for installation, as well as fastening beams using a table (Fig. IV-19, b), which takes all the supporting pressure.
Bolts or welds along the wall are needed to keep the secondary beams from tipping over and the main beam from buckling. In the latter respect, the fastening of the beams to the rib is more efficient than to the table.
The fastenings of freely adjoining beams are calculated on the support pressure A, increased by 20-30%. This takes into account the presence of minor moments in the support attachments. With a large value of the moments, their influence should be taken into account by calculation.
An example of a rigid connection of beams at the same level, which ensures the transfer of not only support pressures, but also support moments, is shown in Figure IV-20. Attaching the upper chord of the auxiliary beam to the pad (called a "fish") and the lower chord to the table should be designed for force
where M0 is the support moment of the beam,
h "is the height of the auxiliary beam.
The horizontal anchoring of the table to the vertical is calculated on the resultant force N and support pressure A, if the wall of the auxiliary beam is not attached directly to the main beam (Fig. IV-20, right), and on part of the support pressure A1, if the wall is attached to the main beam (Fig. . IV-20, left).
The share of the support pressure - A1, transmitted through the table, and the share A2, which is transmitted directly from the wall to the corners, are determined on the assumption of direct proportionality between these forces and the areas of the seams that secure the wall of the auxiliary beam and the console to the main beam.
The welds that attach the table to the main beam must be designed for the operating pressure A and the moment M = Ae-Nz, where e is the eccentricity of application of the force A; z - distance from force N to the center of gravity of the calculated welds.
An example of a rigid welded joint at a lowered level is shown in Figure IV-21. The fastening of double-walled beams is complicated by the fact that in their support sections there are support pressures and moments not only in the vertical plane, but also in the horizontal plane, as well as torques. An example of attaching a double-skinned crane bridge girder to an end girder is shown in Figure IV-22. Both walls 1 of the crane girder are welded to the wall of the end girder using vertical overlays 2. In the places where the walls of the crane girder adjoin to the end girder between the walls 3 of the latter, diaphragms 4 should be placed 4. The belts of the crane girder in the assembly are replaced or covered with nodal gussets 5 expanding at an angle of 45 °. In high-speed cranes, the free edges of the nodal gussets 5 are rounded off and ensure smooth adhesion of the edges of the gusset to the belts of the beams to be connected. Crane girder chords can be end-to-end welded directly to the end girder chords. For the rigidity of the node, in this case, inserts in the form of an isosceles triangle with a leg length and not less than the width of a wider belt of the connected beams are placed between the chords of both beams.
When calculating such connections, it is conventionally considered that the vertical seams between the walls and the linings (w-1 and w-2) work on the vertical support pressure Av of the adjacent beam. Horizontal seams between chords and nodal inserts (w-3) work for vertical and horizontal moments and horizontal support pressures of the adjacent beam.
When calculating such connections, it is conventionally considered that the vertical seams (w-1 and w-2) between the walls (1 and 3) and the overlays (2) work to transfer the supporting vertical pressure Av of the adjoining beam. In fact, these seams also perceive some proportion of bending vertical and horizontal moments. This circumstance is taken into account by increasing the reference pressure by 20-30%. When calculating the seams, it is also necessary to take into account the effect of the constructive moment M "= Avbn, where bn is the width of the vertical lining (the distance between the seams w-1 and w-2).
It is also conventionally considered that the horizontal seams (w-3 and w-4) between the nodal gussets and the chords of the beams to be connected work on the supporting horizontal pressure Ag of the adjoining beam (without an increase of 20-30%) and on bending moments acting in the vertical and horizontal (Мв and Мг) planes. The total edge stresses in the weld (w-3) can be approximately checked by the formula:
where Fshz is the area of one horizontal seam (w-3) between the nodal gusset and the belt of the adjacent beam;
Wshz - moment of resistance of the same seam;
hп is the distance between the centers of gravity of the chords of the adjoining beam.
An example of the graphic design of a welded single-wall beam is shown in Figure IV-23.